1. Technical Field
The technical field relates to an imaging apparatus for generating image data based on an optical subject image by means of an imaging device, and more particularly to the imaging apparatus adopting an electronic front curtain as a shutter means.
2. Related Art
Resetting electric charges of an imaging device per line allows a function similar to a front curtain of a mechanical shutter to be realized. Such exposure control is occasionally called “electronic front curtain”. In this case, only a rear curtain is driven in the mechanical shutter for the exposure. An exposure time is determined by a time elapsing from resetting of electric charges of the imaging device per line to running of the rear curtain of the mechanical shutter. Therefore, by determining a timing at which the electric charges of the imaging device per line is reset according to running characteristics of the rear curtain of the mechanical shutter, the exposure time on all the lines can be maintained constant.
The mechanical shutter is spaced from the imaging device in a direction of an optical system. Therefore, a light shielding position on the imaging device with the rear curtain of the mechanical shutter changes according to influences of a focal distance, an exit pupil distance of an optical system, and the like. For this reason, when reset characteristics of the electronic front curtain for all lines are made constant according to the characteristics of the mechanical shutter, uneven exposure amount occurs depending on regions of the imaging device.
The imaging apparatus described in JP2007-53742A controls a time elapsing from the resetting of electric charges of the imaging device in each line to the running of the rear curtain of the mechanical shutter on the respective line to vary according to the regions of the imaging device. This arrangement can reduce uneven exposure amount on the regions of the imaging device.
The imaging apparatus disclosed in JP2007-53742A determines a scanning curve pattern of the electronic front curtain based on a focal distance, an exit pupil distance, an aperture value, and a focus position of the optical system. However, the exit pupil distance may change due to an imaging condition and an image height on the imaging device. Further, brightness unevenness might occur due to vignetting, but an influence of the vignetting is not taken into consideration by JP2007-53742A.